Polyamides are known as engineering plastics and has enjoyed wide applications. It has been known that the mechanical characteristics of polyamides are improved by mixing a filler such as glass. A method which has been used widely for preparing such a glass-polyamide composite comprises kneading a fusible polyamide such as an aliphatic polyamide including nylon 66 and glass fiber, typically chopped strands, in an extruder, etc. According to this method, a composite is prepared by heating separately prepared polyamide to high temperature above the melting point. However, glass fiber is not dispersed uniformly in the polyamide matrix so that the degree of improvement, e.g., an increase in hardness or a reduction in linear thermal expansion coefficient is not sufficient. Besides, the method is inapplicable to non-fusible aromatic polyamide.
Water glass is one of the most inexpensive inorganic materials. Water glass can be seen as glass having the simplest composition. Abundant in nature and well supplied, it is useful as a raw material for detergents, soil stabilizers, fire proofing agents, refractory cement, silica gel, and the like.
However, if water glass, which has a high alkali metal content, is mixed into polyamide as a filler in accordance with the conventional method, it fails to afford sufficient mechanical characteristics or electrically insulating properties on account of its strong character as an alkali metal salt. In addition, an alkali metal present in a glass composition tends to be converted to a hydroxide or a carbonate, which will destroy the chemical structure of glass.
U.S. Pat. Nos. 3,006,899, 3,063,966, 2,708,617, and 2,831,834 describe synthesis of polyamides by interfacial polymerization with no reference to preparation of a composite with glass. U.S. Pat. No. 3,708,456 discloses preparation of a composite comprising interfacial polymerization in the presence of inorganic fiber such as silica. According to U.S. Pat. No. 3,708,456, previously prepared inorganic fibers having a relatively large size are incorporated into polyamide, failing to be finely dispersed in the polyamide matrix. The resulting composite shows insufficient improvement in thermal and mechanical characteristics and suffers from considerable anisotropy in manifestation of the characteristics due to the shape of the fibers.